Signal transducer



Dec. 6, 1966 Filed April 16, 1962 J. E. SCOTT 3,290,487

SIGNAL TRANSDUCER 2 Sheets-Sheet l REFERENCE PHASE cg 35 DETECTOR L f 26 32 OUTPUT S|GNAL STZ N'EE Eli-i- A AND B RESULTANT a B A i .E i 42 RESXE'ANT 1 1 2 c C 44 5 i a 48 B RESULTANT I K1 K2 F I G 4 INVENTOR. L/OHN E. Scorr BY FIG. 2. a 4%:

ATTORNEY Dec. 6, 1966- J. E. sco'r'r SIGNAL TRANSDUCER 2 Sheets-Sheet 2 Filed April 16, 1962 FIG. 5b.

FIG.50.

FIG. 6.

INVENTOR. JOHN 5 $60 2' r BY OUTPUT SIGNAL ATTORNEY United States Patent ware Filed Apr. 16, 1962, Ser. No. 187,668 12 Claims. (Cl. 235-6111) This invention relates in general to transducers and more particularly to such transducers as provide signals having phases and amplitudes respectively representing the senses and magnitudes of displacements of elements with respect to other elements.

Differential, or E, transformers such as is shown in FIGS. 3-1, Servomechanism Practice, William R. Ahrendt, McGraw-Hill Book Company, Inc., New York, are transducers of the aforementioned type and are each provided with an excitation primary winding and two secondary windings so connected that their respective induced signals subtractively combine. Inductive coupling between the excitation winding and each of the secondary windings is varied simultaneously by moving a permeable armature in opposite directions with respect to both secondary windings. As a result, the output signal across one secondary winding increases and the output signal across the other secondary winding decreases, thereby providing a difference signal having an amplitude proportional to the displacement of the armature from a null position and a phase depending on the sense of such displacement.

Apparatus embodying the present invention provides a differential transformer type output signal, i.e. one that has a meaningful amplitude and phase, without need for simultaneously changing two coeflicients of inductive coupling (moving an armature with respect to two secondary windings) and, instead, requires that only the coefficient of coupling between one secondary winding and its primary excitation winding be variable. 1

Apparatus embodying the present invention requires two transformers, one of which has the aforesaid variable coefficient of coupling and the other of which has a constant coeflicient of coupling between its primary and secondary windings (which can be matched :by the variable coupling coefficient). With the variable coupling set so that the difference between the output signals across the two secondary windings is zero, increasing the coupling between the primary and secondary windings of the transformer with the variable coupling causes the amplitude of the difference signal to be proportional to such increase and of one phase, while decreasing such variable coupling causes the difference signal to be of an opposite phase, but with an amplitude proportional to such coupling decrease.

By requiring the coupling between the windings of only one of two transformers to be variable, apparatus embodying the present invention may be made structurally small and thereby find wide application, several examples of which are described in detail later.

A principal object of the invention is to provide a transducer capable of producing an output signal having an amplitude and phase dependent solely on the inductive coupling which exists between the primary and secondary windings of only one transformer.

Another object of the invention is to provide a transducer capable of producing an output signal having an amplitude and phase respectively dependent on the amount and direction that one member moves with respect to another.

Another object of the invention is to provide a read head for use with magnetic storage devices that produces an output signal, the polarity of which depends on whether Patented Dec. 6, 1966 ice a ONE or a ZERO is being read, and can utilize a conventional C-shaped core therefor.

The invention will be described with reference to the figures wherein:

FIG. 1 is a schematic diagram of a circuit embodying the invention,

FIG. 2 is a diagram useful in describing the operation of the circuit of FIG. 1,

FIG. 3 is a schematic diagram of one species of the invention,

FIG. 4 is a schematic diagram of a circuit which embodies the present invention and is useful in a magnetic storage medium,

FIGS. 5a and 5b are diagrams useful in describing two ways in which the circuit of FIG. 4 may be employed, and

FIG. 6 is a schematic form of another species of the invention.

Referring to FIG. 1, a transformer 10 is provided with a constant coeflicient of inductive coupling K between its primary winding 12 and its secondary winding 14. A second transformer 16 adapted to have a variable coefficient of coupling K between its primary and secondary windings, respectively designated 18 and 20, has such coefficient K varied by changing the reluctance between the primary winding 18 and the secondary Winding 20. The winding 18 is wound counter to the winding 12 and serially connected thereto as shown, thereby causing the signals at the upper and lower portions of the windings 12 and 18 respectively to be always of the same sense when excited in the manner depicted. Normally the coefficients of coupling K and K are equal, with the coefficient K being, of course, permitted to be both greater and less than the coeflicient K The secondary windings 14 and 20 are connected in series with each other and have their resultant induced voltage applied to a phase detector 21, e.g. the phase detector shown and described in Electronic and Radio Engineering, Frederick E. Terman, page 1010, McGraw-Hill Book Co., New York, which receives also the excitation signal as a phase reference signal. The D.C. output signals from the phase detector are applied to a galvanometer 22, the needle of which deflects according to the phase and magnitude of the signal applied to the detector 21. (Counterwinding the secondary windings 14 and 20 or inserting an inverter into one of the leads from the excitation source will serve the same function as the aforementioned primary counterwinding.)

With the coupling between the primary and secondary windings of the transformer 16 set so that K =K the points A and B of FIG. 1 simultaneously go equally positive and then equally negative with respect to point 0 periodically on application of an applied A.C. signal. This is because the transformers 10 and 16 are electrically identical and produce equal magnitude secondary winding voltages when their respective coefficients of coupling are the same. As a result, the resultant voltage taken across points A and B is zero as shown in the second graph of FIG. 2. Should the coupling K be reduced so that coupling K becomes substantially greater, the voltage appearing between point A and point 0 will be greater than the voltage appearing between point B and point 0 thereby causing a resultant voltage A-B (see the third graph of FIG. 2) of a particular phase to be developed across points A and B. This resultant voltage then causes the meter 22 needle to deflect in a particular direction, the amount of deflection being proportional to the difference between K and K Should the transformer 16 have its coupling set so that K is greater than K the voltage developed at point B will be substantially greater than the voltage developed at point A, thereby causing the resultant voltage AB to be of a phase (see the fourth graph of FIG. 2) which is opposite to that when the coupling K is greater than the coupling K This last-mentioned resultant voltage then causes the meter 22 needle to deflect in proportion to the difference between K and K but in a direction opposite to that herebefore mentioned. Hence, it is seen that a differential transformer type output signal is provided without the prior art need for simultaneously varying two coeflicients of inductive coupling.

FIG. 3 shows two transformers 24 and 26 electrically connected (in a manner identical to the way the transformers 10 and 16 of FIG. 1 were connected) to utilize the present invention as a sensor in detecting the magnitude and direction that a gyro 28 moves relative to a fixed reference, i.e. its case. The transformer 24 has a constant coupling coefiicient between its windings; on the other hand, the transformer 26 has a C-shaped core 30 (adapted to be secured to the gyro case) which provides a variable coupling coefficient depending on the reluctance of the material brought into adjacency with its gap 32. A strip of permeable material 29 is secured to the gyro 28 and so positioned that the electrical characteristics of the transformers 24 and 26 are identical when only part of the strip 29 is adjacent the gap 32. Rotation of the gyro 28 clockwise brings more permeable material near the [gap 32 and there-by causes the transformer 26 secondary winding to produce a larger output signal than the transformer 24 secondary winding; rotation of the gyro 28 counterclockwise takes the permeable material 29 out of adjacency with the gap 32, thereby causing the output signal from the transformer 24 secondary winding to be greater than the output signal from the transformer 26 secondary winding. Hence, the output difference signal taken across the leads 34 and 36 will have a phase dependent upon the direction of rotation of the gyro 28 and an amplitude proportional to the amount of sudh rotation.

Referring to FIG. 4, the invention is shown embodied in a data storage medium. A pulse driven amplifier 38 applies its output pulse simultaneously to the serially connected primary windings of transformers 40 and 42. A load 44 has developed thereacross a voltage proportional to the difference between the voltages induced in the serially connected secondary windings of the transformers 40 and 42. The voltage developed across the load 44 is applied to an amplifier 46. The core of the transformer 42 is shaped like the core 30 of FIG. 3, and a magnetic storage tape 48, when brought adjacent the gap in the transformer 42 core, operates to change the coupling .between the primary and secondary windings of the transformer depending on the tape storage technique employed. Two such storage techniques will be described below to illustrate the operation of the apparatus of FIG. 4.

In the first storage technique: the tape 48 is provided with permeable saturated and unsaturated elements repre senting respectively ZEROS and ONES. (If desired the saturated and unsaturated elements may be replaced by nonpermeable and permeable elements.) The unsaturated elements make the coefiicient of coupling between the transformer 42 windings greater than that between the windings of the transformer 40 when they .are adjacent the transformer 42 core gap; the saturated elements make the coefficient of coupling between the transformer 42 windings less than that between the windings of the transformer 40 when they are adjacent the transformer 42 core gap. Hence, when half of a saturated and half of an unsaturated element is adjacent the transformer 42 core gap, the transformers 40 and 42 are electrically identical. Referring now to FIG. a, the core gap is shown first adjacent a ONE element and then adjacent a ZERO element. With the core gap in the ONE situation, a negative pulse appearing across A of FIG. 4 causes a positive pulse to be developed across the secondary winding of the transformer 40 and a substantially larger positive pulse to be developed across the secondary winding of the transformer 42 as a result of the greater coupling in this transformer. As a result, current flows in the serially connected secondary winding circuits in a particular direction through the load 44, thereby causing a negative going pulse, ie a ONE pulse, to be developed thereacross. With the core gap of FIG. 5a in the ZERO situation, the negative going pulse applied across A causes a larger positive going pulse to be developed across the secondary winding of the transformer 40 than across the secondary Winding of the transformer 42. As a result, current flows in the serially connected secondary winding circuits in a direction which is opposite to the direction that the current flowed when the core gap was in its ONE situation, thereby causing a positive going or ZERO pulse to be developed across the load 44.

In the second storage technique: When the transformer 42'core gap is adjacent an unsaturated element of the tape 48, the coefiicient of coupling between the transformer 40 primary and secondary windings is exactly the same as the coefiicient of coupling between the pri-' mary and secondary windings of the transformer 42; this condition is a ZERO situation. A ONE situation results when the transformer 42 core gap is adjacent a saturated tape element, i.e. when the transformer 40 windings are closer coupled than the transformer 42 windings. (As before, magnetic and nonmagnetic elements may be substituted respectively for unsaturated and saturated elements.) With application of a negative going pulse across A and the core gap adjacent an unsaturated element, equal voltages are developed across the transformer secondary windings and no signal across D of FIG. 4. With, however, a core gap in a "ONE situation, i.e. adjacent a saturated tape element, the transformers 40 and 42 are not electrically identical and application of a negative going pulse across A causes a larger positive going pulse to appear across the transformer 40 secondary winding and across the secondary winding of the transformer 42. As a result, current is induced to flow through the load 44 thereby causing a positive ONE pulse to appear across D. Hence, a pulse appearing across D indicates that a ONE element is adjacent the core gap and no pulse appearing across D indicates that a ZERO element is adjacent the gap.

The apparatus of FIG. 4 has the following advantages: (1) Stored data is unambiguously read by providing either positive and negative going pulses to signify respectively ONES and ZEROS, or pulses and no pulses to signify ONES and ZEROS respectively. (2) A writing function may be provided (in addition to the reading function) by mere application of substantial pulses to point A, i.e. by applying pulses thereto which can effectively saturate tape elements. (3) Tape reading may be performed without the ordinarily required relative movement between the tape elements and core gap.

FIG. 6 shows a differential, or E-, transformer embodying the present invention and having an excitation winding 50 inductively coupled to two secondary windings 52 and 54 in conventional manner. An armature 56 is adapted to be so positioned to the right of the line XX that the coefficients of coupling between the excitation winding and both secondary windings are equal. Movement of the armature from its established null position then causes the resultant output signal developed across the secondary windings to be proportional to and of a sense dependent on the manner in which the armature 56 moves. With such a transformer the armature, unlike those of prior art transformers, is unrestricted as to its movement (so long as it remains to the right of the line X-X); further, the armature 56 may be made quite small, thereby avoiding problems inherent in such prior art differential transformers which relate to armature inertia.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is:

1. Apparatus for producing a signal having an amplitude and sense respectively representative of the magnitude and direction of a vector comprising a first transformer having a constant coefficient of coupling between its windings, a second transformer having a variable coefficient of coupling between its windings, the range of variation of which includes the coefiicient of coupling between said first transformer windings, means algebraically adding the output signals on the secondary windings of said transformers, the primary windings of said transformers being connected to produce out-of-phase signals across the transformer secondary windings and being adapted to receive equal amplitude excitation signals, and means responsive to vary the coefficient of coupling between said second transformer windings in proportion to and of a sense representative of said vector, whereby said algebraic sum signal has an amplitude and sense representative of the vector.

2. Apparatus for producing a signal representative of the magnitude and direction that a variable changes comprising first and second transformer means having respective primary and secondary windings, the inductive coupling between said first transformer means windings being substantially constant and the inductive coupling between said second transformer means windings being variable within a range that includes an amount of coupling equal to that between the first transformer means windings, said primary windings being adapted to be excited to induce equal but opposite phase signals across said secondary windings when said inductive couplings are equal, means adapted to vary said variable coupling from an amount that is equal to the coupling of said first transformer means in proportion to the magnitude and direction that said variable changes, and means algebraically adding the secondary winding signals to produce a sum signal, said sum signal having a phase and amplitude respectively representative of the sense and magnitude that said variable changes.

3. Apparatus for producing a signal representative of the motion of one element with respect to another comprising a first transformer having a constant coefficient of coupling between its windings, a second transformer having a permeable core with a discontinuity therein on which its windings are wound, permeable means positionable with respect to said discontinuity and having a null position at which both said transformers have equal coefiicients of coupling, means algebraically adding the output signals on the secondary windings of said transformers, the primary windings of said transformers being connected to produce opposite phase signals across the secondary windings and being adapted to receive equal amplitude signals, said second transformer core being secured to one element and said permeable means being secured to said other element, whereby said algebraic sum signal has an amplitude and sense representative of said motion.

4. Apparatus for producing a signal representative of the motion of one element with respect to another comprising a first transformer having a constant coefiicient of coupling between its windings, a second transformer having a permeable core, said core forming a discontinuous loop and having the windings of said second transformer wound thereon, permeable means positionable with respect to the discontinuity in said core having a null position at which both said transformers have equal coefficients of coupling, means algebraically adding the output signals on the secondary windings of said transformers, the primary windings of said transformers being connected to produce opposite phase signals across the secondary windings and being adapted to receive equal amplitude signals, said second transformer core being secured to one element and said permeable means being secured to said other element, whereby said algebraic sum signal has an amplitude and sense representative of said motion.

5. Apparatus for use with data storage devices wherein digital data is stored by elements which can or cannot be magnetized depending on whether those elements are storing ONES or ZEROS comprising a first transformer having a substantially constant coefficient of inductive coupling between its windings, a second transformer having a permeable core, said core forming a discontinuous loop and having the second transformer windings thereon, means positioning said storage elements adjacent the discontinuity in said second transformer core, whereby the coefiicient of coupling between said second transformer windings equals the coefficient of coupling between said first transformer windings when one kind of element has a particular degree of adjacency with respect to the core discontinuity, means algebraically adding the output signals on the secondary windings of said transformers, the primary windings of said transformers being connected to produce opposite phase signals across the secondary windings and being adapted to receive equal amplitude signals, whereby the algebraic sum signal has a sense indicative of the storage element adjacent the discontinuity in the core of said second transformer.

6. Apparatus for determining the nature of data stored in a magnetic medium, said data being stored by data elements which appear magnetically conductive or inert depending on the nature of the data that they store, comprising a first transformer having a constant coefficient of coupling between its windings, a second transformer having a permeable core with a discontinuity therein on which its windings are wound, means positioning the data elements with respect to said discontinuity, whereby both transformers have equal coefficients of coupling when a portion of one kind of data element occupies a particular position with respect to the discontinuity, means algebraically adding the output signals on the secondary windings of said transformers, the primary windings of said transformers being connected to produce opposite phase .signals across the secondary wind ings and being adapted to receive equal amplitude signals, whereby said algebraic sum signal :has a sense representative of the data element which has said particular position with respect to the discontinuity.

7. Apparatus for use with data storage devices wherein digital data is stored by permeable or nonpermeable elements depending on whether those elements are storing ONES or ZEROES comprising a first transformer having a substantially constant coefficient of inductive coupling between its windings, a second transformer having a permeable core, said core forming a discontinuous loop and having the second transformer windings thereon, means positioning said storage elements adjacent the discontinuity in said second transformer core, whereby the coefficient of coupling between said second transformer windings equals the coefficient of coupling between said first transformer windings when one kind of element has a particular degree of adjacency with respect to the core discontinuity, means algebraically adding the output signals on the secondary windings of said transformers, the primary windings of said transformers being connected to produce opposite phase signals across the secondary windings and being adapted to receive equal amplitude signals, whereby the algebraic sum signal has a sense indicative of the storage element adjacent the discontinuity in the core of said second transformer.

8. Apparatus for use with data storage devices wherein digital data is stored by elements which can or cannot be magnetized depending on whether those elements are storing ONES or ZEROS comprising a first transformer having a substantially constant coefiicient of inductive coupling between its windings, a second transformer having a permeable core, said core forming a discontinuous loop and having the second transformer windings thereon, means positioning said storage elements adjacent the discontinuity in said second transformer core, whereby the coefiicient of coupling between said second transformer windings equals the coefficient of coupling between said first transformer windings when half of each kind of element is adjacent said core discontinuity, means algebraically adding the output signals on the secondary windings of said transformers, the primary windings of said transformers being connected to produce opposite phase signals across the secondary windings and being adapted to receive equal amplitude signals, whereby the algebraic sum signal has a sense indicative of the storage element adjacent the discontinuity in the core of said second transformer.

9. Apparatus for use with data storage devices wherein digital data is stored by substantially saturated or unsaturated elements depending on whether those elements are storing ONES or ZEROS comprising a first transformer having a substantially constant coefiicient of inductive coupling between its windings, a second transformer having a permeable core, said core forming a discontinuous loop and having the second transformer windings thereon, means positioning said storage elements adjacent the discontinuity in said second transformer core, whereby the coefiicient of coupling between said second transformer windings equals the coefiicient of coupling between said first transformer windings when one kind of element has a particular degree of adjacency with respect to the core discontinuity, means algebraically adding the output signals on the secondary windings of said transformers, the primary windings of said transformers being connected to produce opposite phase signals across the secondary windings and being adapted to receive equal amplitude signals, whereby the algebraic sum signal has a sense indicative of the storage element adjacent the discontinuity in the core of said second transformer.

10. Apparatus for use with data storage devices wherein digital data is stored by substantially saturated or unsaturated elements depending on whether those elements are storing ONES or ZEROS comprising a first transformer having a substantially constant coefiicient of inductive coupling between its windings, a second transformer having a permeable core, said core forming a discontinuous loop and having the second transformer windings thereon, means positioning said storage elements adjacent the discontinuity in said second transformer core, whereby the coefiicient of coupling between said second transformer windings equals the coefficient of coupling between said first transformer windings when half of each kind of element is adjacent said core discontinuity, means algebraically adding the output signals on the secondary windings of said transformers, the primary windings of said transformers being connected to produce opposite phase signals across the secondary windings and being adapted to receive equal amplitude signals, whereby the algebraic sum signal has a sense indicative of the storage element adjacent the discontinuity in the core of said second transformer.

11. Apparatus for use with data storage devices wherein digital data is stored by elements which can or cannot be magnetized depending on whether those elements are storing ONES or ZEROS comprising a first transformer having a substantially constant coefiicient of inductive coupling between its windings, a second transformer having a permeable core, said core forming a discontinuous loop and having the second transformer windings thereon, means positioning said storage elements adjacent the discontinuity in said second transformer core, whereby the coefficient of coupling between said second transformer windings equals the coefiicient of coupling between said first transformer windings, when one kind of element is solely adjacent the core discontinuity, means algebraically adding the output signals on the secondary windings of said transformers, the primary windings of said transformers being connected to produce opposite phase signals across the secondary windings and being adapted to receive equal amplitude signals, whereby the algebraic sum signal has a sense indicative of the storage element adjacent the discontinuity in the core of said second transformer.

12. Apparatus for use with data storage devices wherein digital data is stored by permeable or nonpermeable elements depending on whether those elements are storing ONES or ZEROS comprising a first transformer having a substantially constant coefficient of inductive coupling between its windings, a second transformer having a permeable core, said core forming a discontinuous loop and having the second transformer windings thereon, means positioning said storage elements adjacent the discontinuity in said second transformer core, whereby the coefiicient of coupling between said second transformer windings equals the coefiicient of coupling between said first transformer windings when half of each kind of element is adjacent said core discontinuity, means algebraically adding the output signals on the secondary windings of said transformers, the primary windings of said transformers being connected to produce opposite phase signals across the secondary windings and being adapted to receive equal amplitude signals, whereby the algebraic sum signal has a sense indicative of the storage element adjacent the discontinuity in the core of said second transformer.

References Cited by the Examiner UNITED STATES PATENTS 2,722,569 11/ 1955 Loper 340174.1 2,918,535 12/1959 Wiegand 340174.1 2,947,929 8/1960 Bower 340-3473 3,03 8,345 6/1962 Hoeppner et al 340347 3,045,220 7/1962 Anderson 340174.1

MAYNARD R. WILBUR, Primary Examiner. MALCOLM A. MORRISON, Examiner. D. W. COOK, Assistant Examiner. 

6. APPARATUS FOR DETERMINING THE NATURE OF DATA STORED IN A MAGNETIC MEDIUM, SAID DATA BEING STORED BY DATA ELEMENTS WHICH APPEAR MAGNETICALLY CONDUCTIVE OR INERT DEPENDING ON THE NATURE OF THE DATA THAT THEY STORE, COMPRISING A FIRST TRANSFORMER HAVING A CONSTANT COEFFICIENT OF COUPLING BETWEEN ITS WINDING, A SECOND TRANSFORMER HAVING A PERMEABLE CORE WITH A DISCONTINUITY THEREIN IN WHICH ITS WINDINGS ARE WOUND, MEANS POSITIONING THE DATA ELEMENTS WITH RESPECT TO SAID DISCONTINUITY, WHEREBY BOTH TRANSFORMERS HAVE EQUAL COEFFICIENTS OF COUPLING WHEN A PORTION OF ONE KIND OF DATA ELEMENTS OCCUPIES A PARTICULAR POSITION WITH RESPECT TO THE DISCONTINUITY, MEANS ALGEBRAICALLY ADDING THE OUTPUT SIGNALS ON THE SECONDARY WINDINGS OF SAID TRANSFORMERS, THE PRIMARY WINDINS OF SAID TRANSFORMERS BEING CONNECTED TO PRODUCE OPPOSITE PHASE SIGNALS ACROSS THE SECONDARY WINDINGS AND BEING ADAPTED TO RECEIVE EQUAL AMPLITUDE SIGNALS, WHEREBY SAID ALGEBRAIC SUM SIGNALL HAS A SENSE REPRESENTATIVE OF THE DATA ELEMENT WHICH HAS SAID PARTICULAR POSITION WITH RESPECT TO THE DISCONTINUITY. 